Field of the Invention
The present invention relates to a panel member, an aircraft main wing, and a method for forming the panel member.
Description of the Related Art
For an aircraft main wing, the outer surface thereof is formed by a panel-form member (hereinafter, referred to as a wing panel). This wing panel is configured so that the thickness thereof is set according to the portion of the wing. That is, in the base end portion on the airframe side of main wing, and in the portion around the engine-mounting position, the thickness of wing panel is set so as to be large because high strength is required in these portions. In contrast, in the tip end portion of wing or the like portions, the thickness of wing panel is set so as to be small. Thus, the thickness of wing panel is prevented from being increased than necessary while a necessary strength is ensured depending on the respective portions, whereby the weight of wing panel is restrained.
Some wing panels are formed by being machined out of a metallic base material (for example, refer to Takeshi Yamada et al. “Development of Shot Peen Forming Technology of Main Wing Integral Skin of Continental Business Jet” Mitsubishi Heavy Industries Technical Review, Vol. 39, No. 1 (2002), p. 36).
For such a wing panel, to make the thickness thereof different according to the portions, generally, in a portion in which the thickness changes, the position of the cutting tool of a cutting machine with respect to the metallic base material is changed stepwise.
Unfortunately, in the case where the wing panel is machined out of a material, a machining tolerance exists depending on the capability or the like of the cutting machine. In the portion in which the thickness changes, the change amount of the thickness must be set to a dimension equal to or larger than the machining tolerance. In the case where the machining tolerance is, for example, ±0.1 mm, the thickness is preferably increased or decreased stepwise for each dimension equal to or larger than the machining tolerance, for example, for each dimension equal to or larger than 0.2 mm (this increasing/decreasing amount is referred to as a step amount as appropriate). That is, in the case where the design value of thickness in a certain portion P1 of a wing panel 1 is 6.0 mm as shown in FIGS. 4 and 5, the actual dimension after machining of the portion P1 is 6.0±0.1 mm=5.9 to 6.1 mm. In the case where the step amount of thickness in a portion P2 adjacent to the portion P1 is 0.1 mm, which is equal to the machining tolerance, the design value of thickness in the portion P2 is 6.1 mm, and the actual dimension after machining is 6.1±0.1 mm=6.0 to 6.2 mm.
In such a case, as shown in FIG. 5, although the thickness increases from the portion P1 to the portion P2 in design, actually, in some cases, the thickness does not change, or inversely the thickness decreases from the portion P1 to the portion P2. Even in such a case, no problem occurs in terms of strength as long as the thicknesses of the portions P1 and P2 are within the machining tolerance. However, a hindrance may occur in the manufacturing process.
At the site of manufacturing process, the wing panel machined out of a metallic base material by cutting machine is inspected at least visually. If a flaw or the like induced while machining is present on the wing panel, the surroundings of the flaw must be sanded to correct the flaw to the predefined standard or higher grade.
If the step amount of thickness is small, the step existing in the portion in which the thickness changes becomes a minor step, and therefore, at the inspection time, it is sometimes impossible to distinguish between a normal step and a flaw. For this reason, correction is sometimes made as the result of mistaking the normal step for a flaw, which leads to an increase in the manufacturing cost.
To overcome this problem, conventionally, by setting the step amount of thickness to a dimension larger than the machining tolerance as described above, measures have been taken such that a step formed in the portion in which the thickness changes can be checked visually with ease. Thereby, the correction is prevented from being made as the result of mistaking the normal step for a flaw, and thereby the increase in the manufacturing cost is restrained.
Unfortunately, if the step amount of thickness is made larger than the machining tolerance, a portion having a thickness larger than necessary is produced, which leads to an increase in weight of the wing panel. For example, in the above-described example, in the case where the step amount of thickness in the portion P2 adjacent to the portion P1 is made 0.4 mm, which is larger than the machining tolerance, the design value of thickness in the portion P2 becomes 6.4 mm, so that the actual dimension after machining becomes 6.4±0.1 mm=6.3 to 6.5 mm. Therefore, in the boundary portion between the portion P1 and the portion P2, a step of at least 0.1 mm arises. However, in the portion P2, assuming that the above-described thickness of 6.1 mm provides a necessary strength, the thickness design value of 6.4 mm is an excess value by 0.3 mm.